Color television system



Jan. 26, 1943. P, J -r COLOR TELEVISION'SYSTEM 4 Sheets-Sheet 1 Filed March 7, 1941 FIG.

HEAD

AMPLIFIER PHASE INVERTER MITTER TRANS- COMBINING 5| E CIRCUIT 27 AMPLIFIER INVENTOR PHIILIP J. HERBST- ATTOREY L.F.SCANN|NG GENERATOR GENERATOR SYNCHRONIZIN PUISE GENERATOR DELAY NETWORK Jan. 26, 1943. P. J. HERBST 2,309,506

COLOR TELEVI S ION SYSTEM Filed March 7, 1941 4 Sheets-Sheet 2 FIG. 2

'I L'M'IER. B iQ- D -1 O- J (D) 9J1 H (E) TIM E- INVENTOR J. HERBST Jan. 26, 1943'.

ulFFF Filed March 7, 1941 4 Sheets-Sheet 3 L.F.SCANN|NG so -GENERATOR: 6|

70 7| RECEIVER r62 HESCANMNG GENERATOR 5 AMPLIFIER 9+ 95 FIG.5

F TFF FTFFHF F F (X) F F FLFLJF F F F (Y) TIME INVENTOR P lLlP J. HERBST ATTORNEY Jan. 26, 1943. J R sT 2,309,505

COLOR TELEVI S ION SYSTEM Filed March 7, 1941 4 Sheets-Sheet 4 FIG.4

TIME

INVENTOR PH P a. HERBST BY vr Patented Jan. 26, 1943 COLOR. TELEVISION SYSTEM Philip J. Herbst, Fort Wayne, Ind., assignor to Farnsworth Television and Radio Corporation,

a corporation of Delaware Application March 7, 1941, Serial No. 382,117

13 Claims.

This invention relates to multichromatic television systems, and particularly to automatic means for maintaining color phasing in such systems.

In multichromatic television systems which embody a single picture-signal generating device at the transmitter and a single picture-reproducing device at the receiver, means must be provided for successively ermitting the light of the.

various colors to actuate the picture-signal genearting device at the transmitter, and at the receiver means must be provided for permitting the picture-reproducing device to produce pictures of the same successive colors. One method of accomplishing this is to employ color discs at the transmitter and at the receiver, the disc at the transmitter filtering the light passing between the object to be televised and the picturesignal generating device, and the disc at the receiver being interposed between the picture-reproducing device and the observer's eye.

These discs must revolve synchronously in order that the color intervals be the same at the transmitter and receiver, and they must also maintain a particular phase relationship in order that the color sequence be the same at the transmitter and the receiver. In previously known arrangements, color phasing has been obtained by a manually operated switch which interrupts the power or the synchronizing signals supplied to the motor driving the disc long enough to permit it to drop in speed until it has the proper phase. Since different degrees of amplification are required for the signal channels corresponding to each color, it is necessary to employ such a phase switch at the transmitter as well as at the receiver.

It is an object of the present invention to provide means for automatically securing correct phasing of both the transmitter and the receiver color discs, without the necessity for any attention by either the transmitter operator or the observer at the receiver.

In accordance with the invention, there is provided a multichromatic television'system comprising a transmitter and a receiver. The transmitter includes means for developing synchronizing signal components, color-selecting means for causing the transmitter successively to produce picture signals corresponding to light of different colors, means associated with the color-selecting means for producing a color signal component once during each color cycle, means responsive to the synchronizing and signal components and the color signal components to produce colorphasing synchronizing components, and means for transmitting the picture signal combined with the synchronizing signal components and the color-phasing synchronizing components. The receiver is responsive to the transmitted signals and includes color-selecting means for causing the receiver successively to reproduce the received picture signals as images of different colors. The receiver also includes means for utilizing the color-phasing synchronizing components to synchronize the operation of the color-selecting means at the receiver with the color-selecting means at the transmitter.

In accordance with a preferred embodiment of the invention, the transmitter may include separate normally blocked channels respestlvely responsive to picture signals corresponding to light of different colors. The color-phasing synchrom'zing components produced at the transmitter may be utilized to render these channels successively operative in synchronisrn with the color-selecting means.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings:

Fig. 1 is a circuit diagram, partly in block form, showing a multichromatic television transmitter embodying the present invention;

Fig. 2 is a graph showing the voltages appearing at various points in the transmitter 01 Fig. 1;

Fig. 3 is a circuit diagram, partly in block form, of a multichromatic television receiver embodying the present invention;

Fig. 4 is a graph showing voltages at various points in the receiver of Fig. 3; and

Fig. 5 is a graph showing one method by which the color sequence pulses may be transmitted.

Referring now more particularly to Fig. 1 of the drawings, there is shown schematically a television transmitter capable of producing and transmitting television signals in three colors. An image of the object i to be transmitted is focused by means of a lens 2 upon the photocathode of a picture-signal generating device 3. A color disc 4, driven by a phonic motor 5, is interposed between the lens 2 and the picturesignal generating device 3. The picture signals produced by the device 3 are supplied through a head amplifier 6 to gain controls 1, 8 and 9, which are connected in the control-grid circuits of vacuum tubes In, H and I 2,respectively. The

cathodes of these tubes are each grounded through a resistor |3 shunted by a condenser I4. The anodes of tubes H), II and |2 are connected to the combining circuit l5, which in turn supplies a transmitter IS.

A timer and synchronizing pulse generator l1 furnishes synchronizing signals to the low-frequency scanning generator iii to which are connected the low-frequency scanning coils l9, and to a high-frequency scanning generator 2|. to which are connected the high-frequency scanning coils 2|. The generator I! also supplies synchronizing pulses to the transmitter I6. The lowfrequency synchronizing pulses from the synchronizing pulse generator I! are also supplied to the phonic motor 5, and to grid 23 of a mixer tube 24.

The color disc 4 is provided with an armature 25 which passes between the pole pieces of an inductance device 26. 'It will be understood that the inductance device 26 may, without departing from the scope of the invention, be replaced by a commutator and brush arrangement or by a photoelectric or electrostatic device adapted to produce suitable pulses. The pulses delevoped by the device 26, after amplification by an amplifier 21, are applied to grid 28 of the tube 24 by way of a condenser 29. Grids 23 and 28 of the tube 24 are each connected to ground by way of a resistor 30, and the cathodes of the tube 24 are connected to ground by way of a resistor 3| shunted by a condenser 32. The combined output of the mixer tube 24, which is developed across load resistor 33, is applied by way of a condenser 34 to grid 35 of a limiter tube 36, Grid 35 is connected to ground by way of a resistor 31, and the cathode of the tube 36 is connected to ground by way of a resistor 38 shunted by a condenser 39. The output of tube 36, which is developed across load resistor 40, is supplied, by way of a condenser 4| and a conventional phase inverter A, to a delay network 22, the output of which is fed to the generator l1, and to a multivibrator 42, which may be of any suitable form, as well known in the art. The multivibrator circuit of one suitable form is shown merely by way of example.

The output of the multivibrator 42 is supplied, by way of a condenser 43, to grid 44 of a limiter tube 45. The grid 44 is grounded through a resistor 46. The cathode of tube 45 is grounded through a resistor 41 shunted by a condenser 48. The output of tube 45, developed across load resistor 49, is applied, by way of a condenser 50, to suppressor grid 5| of the tube In. The tube I is maintained normally inoperative by the application to its suppressor grid by way of a resistor 52, of a negative potential from the point indicated by C-. The suppressor grid is bypassed to ground ,by a condenser 53.

The output of the multivibrator 42 is also supplied. by way of a condenser 54, to a second multivibrator 55, the output of which likewise is applied to the grid of a limiter tube 56 which in turn supplies its output to suppressor grid 5| of the tube Similarly, the output of the multivibrator 55 is also applied, .by way of a condenser 51, to a third multivibrator 58, the output of which likewise is applied to the grid of a limiter tube 59 which in turn supplies its output to suppressor grid 5| of the tube I2. I

The operation of the transmitting system of Fig. 1 may be better understood by reference to Fig. 2, in which all the curves are plotted to the same time base. The picture-signal output of the amplifier 6 is indicated by the curve A. The

pulses produced by the rotation of the color disc 4 and appearing as the output of the amplifier 21 are indicated by the curve B. The low-frequency synchronizing pulses which are applied to the grid 23 of tube 24 are indicated by the curve C. The combination of curves B and C represents the voltage which is developed across the load resistor 33 of the tube 24, and the the form of this voltage is indicated by the curve D. After clipping by the limiter tube 36, the resultant pulses have the form indicated by the curve E. These short pulses cause the multivibrator 42 to produce longer negative pulses, which in turn produce, in the output circuit of the limiter tube 45, long positive pulses of the form shown in curve F. These positive pulses overcome the normal negative bias on the suppressor grid 5| of the tube l0 and thus restore this tube to operativeness during their duration.

The condenser 54 is chosen small enough so that the negative pulses comprising the output of the multivibrator 42 are differentiated. In this manner, the decay of the negative pulses produces short positive pulses suitable for triggering the multivibrator 55. Limiter tube 56, therefore, produces an output having the form shown by curve G. The case is similar with respect to the multivibrator 58, so that limiter tube 59 has an output such as shown by curve H. Thus tubes IO, M and I2 are rendered successively operative.

Let it be assumed that the desired color sequence is red, green and blue, and that the sequence is to begin with red. In this case, the armature 25 is secured on the color disc 4 at such a position that it will pass between the pole pieces of the device 26 when the red color filter is properly positioned between the lens 2 and the picture-signal generating device 3. The resultant pulse, when combined with the lowfrequency synchronizing pulse and after clipping, will provide a pulse which, by means of the multivibrator 42 and limiter tube 45, unblocks the vacuum tube In for an interval corresponding to the transmission time of the red field. When this interval is over, the tube ID will be blocked, and the multivibrator 55 and limiter tube 56 will unblock the tube II for an interval corresponding to the transmission time of the green field. At the end of this interval, the tube II will be blocked and the multivibrator 58 and limiter tube 59 will unblock the tube I2 for an interval corresponding to the transmission time of the blue field. The resultant picture signals, after proper adjustment of their relative levels by the gain controls I, 8 and 9, are supplied to the combining circuit l5 and thence to the transmitter l6 as a single picture signal.

The color-phasing pulses in the output circuit of the ilmiter tube 36 are also supplied to the delay network 22, which may be of conventional design. The output from the delay network 22 controls the keying of the synchronizing pulse generator I! in such a manner that an additional low-frequency synchronizing pulse is de veloped immediately following every third regular low-frequency synchronizing pulse. Hence, the output of the synchronizing pulse generator I! has the form shown in curve X of Fig. 5 once every three fields, and the form shown in curve Y of Fig. 5 the remainder of the time.

It will be understood that other methods, of combining the color-phasing pulses with the regular synchronizing signals may be employed without departing from the scope of the invention. For example, this might be accomplished by extending the length of each third low-frequency synchronizing pulse, by frequency modulating this pulse, by varying the number of serrations comprising this pulse, orby extending the length of the high-frequency synchronizing pulses immediately following this pulse.

The low-frequency pulses supplied by the synchronizing pulse generator I! to the phonic motor serve to keep the disc 4 rotating at the proper synchronous speed. Thus, it will be seen that means are provided for causing the various picture-signal channels to become operative in a cycle having the proper phase with respect to the various color fields being transmitted, and the output signal of the transmitter, in addition to including the usual picture and synchronizing signals, also conveys intelligence regarding the phasing of the color disc.

Referring now i Fig. 3 of the drawings, there is shown in schematc form a television receiving system adapted to receive the television signals produced by the transmitter of Fig. 1. A receiver 60 supplies the picture signals to the picture-reproducing device 6|. The receiver 60 also supplies synchronizing pulses .to a high-frequency scanning generator 62, to which are connected high-frequency scanning coils 63. The low-frequency synchronizing signals from the receiver 60 pass through a, conventional integrating network comprising a condenser 64 and a resistor 65, and are applied to the grid 66 of the phase-inverting tube 61. The grid 66 is biased by a suitable negative potential from the source 0- connected to the resistor 65. The cathode of tube 61 is grounder. The synchronizing impulses developed across load resistor 68 in the output circuit of the tube 61 are supplied, by way of a condenser 69, to a low-frequency scanning generator 10, the output of which is connected to low-frequency scanning coils H.

The synchronizing impulses developed in the output circuit of the tube 61 are also applied to grid 12 of a limiter tube 13. The grid 12 is connected to one terminal of a resistor 14, the other terminal of which is connected to the movable arm of a potentiometer 15 connected between ground and a source of negative potential indicated by C. The cathode of the tube 13 is grounded. The pulses developed across load resistor 16 in the output circuit of tube I3 are applied, by way of a condenser 11, to grid 18 of a mixer tube 19. The grid I8 is connected to ground by way of a resistor 89. The cathodes of the tube 19 are connected to ground by way of a resistor 8| shunted by a condenser 82. Color disc 83, which is driven by phonic motor 84, carries an armature 85 which passes between the pole pieces of an inductance device 86. The latter is connected, through an amplifier 81, to grid 88 of the tube 19. The grid 88 is connected to ground by way of a resistor 89. It will be understood that the inductance device 86 may, without departing from the scope of the invention, be replaced by a commutator and brush arrangement or by a photoelectric or electrostatic device adapted to produce suitable pulses.

The combined impulses which are developed across load resistor 96 in the output circuit of the tube 19 are applied, by way of a condenser 9|, to grid 92 of a tube 93. The grid 92 is connected to one terminal of a resistor 94, the other terminal of which is connected to the movable arm of a, potentiometer 95 connected between ground and a source of negative potential indicated by C.

The cathode of tube 93 is grounded. The pulses developed across load resistor 96 in the output circuit of tube 93 are applied, by way of a condenser 91, to the phonic motor 84.

The operation of the receiving system of Fig. 3 may be more readily understood by reference to the curves of Fig. 4, which are all plotted to the same time base. In the latter figure, the curve A indicates schematically the energy of the fram'- ing and color-phasing pulses in the output of the second detector of the receiver 69. The curve B indicates these pulses after being integrated by the integrating network 6465, the integrated pulses being applied to the grid 66 of the tube 61. The curve 0 indicates the pulses of inverted phase which are present at the point C of Fig. 3. The curve D indicates the wave form at the output of the color-phasing limiter tube 13, and the curve E indicates the amplified pulses produced by the armature and the inductance device 86. The combined output pulses of the tube I9 are indicated by the curve F. These pulses are applied to the grid 92 of the tube 93, thereby producing the series of pulses indicated by the curve G. The latter pulses are employed for synchronizing the phonic motor 84.

It will be apparent, therefore, that the phonic motor 84 receives synchronizing pulses only when the pulses produced by the inductance device 86 (curve E) are in phase with one of the low-frequency synchronizing pulses appearing at the output of the tube 13 (curve D). If the disc 83 does not have the proper phase with respect to the incoming signal, it ispermitted to differ from the synchronized speed for just long enough to reach the proper phase relationship, at which time the synchronizing pulses are again supplied to the phonic motor 84, thereby keeping it in synchronism and in phase from then on.

The curve X of Fig. 5 shows the synchronizing signals during the frame blanking interval which precedes the picture signals corresponding with the first color in the desired color sequence, and curve Y of Fig. 5 shows the synchronizing signals during the frame blanking intervals which precede the picture signals corresponding with either of the other co ors. The solid curve in Fig. 57. shows how the synchronizing signals of Fig. 5X build up to exceed both the low-frequency synchronizing signal level, determined by the bias on the grid 66 of the tube 61 (Fig. 3) and the colorphasing limiter level, determined by the setting of the potentiometer 15, the resultant pulses being those shown. with a different time base, by the curve D of Fig. 4. In Fig. 5Z, the dotted curve shows how the synchronizing signals do not build up sufliciently to exceed the level of the colorphasing limiter tube 13 in the absence of colorphasing signals. This condition is realized when the synchronizing signals have the form shown in curve Y of Fig. 5.

While there has been described what is at present considered the preferred embodiment of the invention. it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A multichromatic television system comprising a transmitter having means for developing synchronizing signal components, color-selecting means for causing said transmitter successively,

to produce picture signals corresponding to light of different colors, means associated with said color-selecting means ior producing a color phase pulse once during each color cycle, mean responsive to said synchronizing signal components and said color phase pulses to produce color-phasing synchronizing components whenever said firstnamed components and said pulses coincide, and means for transmitting said picture signals combined with said synchronizing signal components and said color-phasing synchronizing components; and a receiver responsive to said transmitted signals having color-selecting means for causing said receiver successively to reproduce said picture signals as images of said different colors, and means for utilizing said color-phasing synchronizing components to synchronize the operation of the color-selecting means at said receiver with the color-selecting means at said transmitter.

2. A multichromatic television system comprising a transmitter having means for developing synchronizing pulses, color-selecting means for causing said transmitter successively to produce picture signals corresponding to light of difierent colors. and means for utilizing said color-synchronizing pulses to synchronize the operation of the color-selecting means at said receiver with the color-selecting means at said transmitter,

3. A multichromatic television system comprising a transmitter having means for developing synchronizing pulses, color-selecting means for causing said transmitter successively to produce picture signals corresponding to light of difierent colors, means associated with said color-selecting means for producing a color phase pulse once during each color cycle, means responsive to said synchronizing pulses and said color phase pulses to produce color-synchronizing pulses whenever said synchronizing pulses and said color-phase pulses coincide, and means for transmitting said picture signals combined with said synchronizing pulses and said color-synchronizing pulses; and a receiver responsive to said transmitted signals having color-selecting means for causing said receiver successively to reproduce said picture signals as images of said different colors, and means for utilizing said color-synchronizing pulses to maintain the color-selecting means at said receiver in phase with the color-selecting means at said transmitter.

4. A multichromatic television transmitter comprising means for developing synchronizing signal components, color-selecting means for causing said transmitter successively to produce picture signals corresponding to light of difierent colors, means associated with said color-selecting means for producing a pulse once during each color cycle, means responsive to said synchronizing signal components and said pulses to produce color-phasing pulses whenever said pulses and said synchronizing signal components coincide, means for deriving color-phasing synchronizing components from said color-phase pulses, and means for transmitting said picture signals combined with said synchronizing signal components and said color-phasing synchronizing components.

5. A multichromatic television transmitter comprising means for developing synchronizing pulses, color-selecting means for causing said transmitter successively to produce picture signals corresponding to light of different colors, means associated with said color-selecting means for producing a pulse once during each color cycle, means responsive to said synchronizing pulses and said pulses to produce color-phasing pulses, means for modifying certain ones of said synchronizing pulses in response to said color-phasing pulses and means for transmitting said picture signals combined with said synchronizing pulses and said modified synchronizing pulses.

6. A multichromatic television transmitter comprising means for developing synchronizing signal components, color-selecting means for causing said transmitter successively to produce picture signals corresponding to light of different colors, separate normally blocked channels respectively responsive topicture signals corresponding to light of difierent colors, means "550- ciated with said color-selecting means for producing a signal component once during each color cycle, means for combining said synchronizing signal components and said signal components to produce color-phasing synchronizing components whenever said signal components and said synchronizing signal components coincide, means for utilizing said color-phasing synchronizing components to render said channels successively operative in synchronism with said color-selecting means, means for modifying certain ones of said synchronizing signals in response to said colorphasing synchronizing components, and means for transmitting said picture signals combined with said synchronizing signal components and said modified synchronizing signal components.

'7. A multichromatic television transmitter comprising meansfor developing synchronizing pulses, color-selecting means for causing said transmitter successively to produce picture signals corresponding to light of difl'erent colors, separately normally blocked channels respectively responsive to picture signals corresponding to light of different colors, means associated with said color-selecting means for producing a color phase pulse once during each color cycle, means responsive to said synchronizing pulses and said color phase pulses to produce color-synchronizing pulses, whenever said synchronizing pulses and said phase pulses coincide, means for utilizing said color synchronizing pulses to render said channel successfully operative in synchronism with said color selecting means, means for modifying certain ones of said synchronizing pulses to produce modified pulses of substantially equal amplitude but increased duration, and means for transmitting said picture signals combined with said synchronizing pulses and said modified synchronizing pulses.

8. A multichromatic television receiver comprising means for receiving signals including picture signals representing images of diiferent colors, synchronizing components and modified synchronizing components, means for reproducing said images in multichromatic light in accordance with said picture signals, means responsive to said synchronizing components and said modified synchronizing components for synchronizing said image reproducing means, color selecting means forselecting said different colors from said images in multichromatic light for reproducing said images in difierent colors, and means responsive to said modified synchronizing components only for synchronizing the operation of said color selecting means.

9. A multichromatic television receiver comprising means for receiving signals including picture signals representing images of difierent colors, synchronizing pulses and modified synchronizing pulses of equal amplitude but longer duration, means for reproducing said images in accordance with said picture signals in multichromatic light, means responsive to said synchronizing pulses and said modified synchronizing pulses for synchronizing said image reproducing means, color selecting means for selecting said different colors from said images in multichromatic light for reproducing said images in difierent colors, means including an integrating network and an amplitude filter coupled thereto responsive to said modified synchronizing pulses only for synchronizing the operation of said color selecting means.

10. The method of developing and reproducing a multichromatic television signal which comprises developing synchronizing signal components, successively producing picture signals corresponding to light of different colors, producing a color phase pulse once during each color cycle, combining said synchronizing signal components and said color phase pulses to produce colorphasing synchronizing components whenever said synchronizing signal components and said color phase pulses coincide, utilizing said colorphasing synchronizing components to modify certain ones of said synchronizing signal components, transmitting said picture signals combined with said synchronizing signal components and said modified synchronizing signal components, receiving said transmitted signals, successively reproducing said picture signals as images of said different colors, and utilizing said modified synchronizing signal components to synchronize said reproduction with said production of said picture signals.

11. The method of developing and reproducing a multichromatic television signal which comprises developing synchronizing pulses, succescolor-phasing pulses whenever said pulses and said synchronizing pulses coincide, modifying certain ones of. said synchronizing pulses in response to said color-phasing pulses to produce modified synchronizing pulses of equal amplitude but increased duration, transmitting said picture signals combined with said synchronizing pulses and said modified synchronizing pulses, receiving said transmitted signals, successively reproducing said picture signals as images of said difierent colors, and utilizing said modified synchronizing pulses to synchronize said reproduction with said production of said picture signals.

12. The method of developing a multichromatic television signal which comprises developing synchronizing signal components, successively producing picture signals corresponding to light of different colors, producing a color phase pulse once during each color cycle, combining said synchronizing signal components and said color phase pulses to produce color-phasing synchronizing components whenever said colorphase pulses and said synchronizing signal components coincide, modifying certain ones of said synchronizing signal components in response to said color-phasing synchronizing components, and combining said picture signals with said synchronizing signal components and said modified synchronizing signal components.

13. The method of developing a multichromatic television signal which comprises developing synchronizing pulses, successively producing picture signals corresponding to light of different colors, producing a pulse once during each cycle,

combining said synchronizing pulses and said colorpulses to produce color-phasing pulses whenever said pulses and said synchronizing pulses coincide, modifying certain ones of said synchronizing pulses in response to said colorphasing pulses to produce modified synchronize ing pulses of equal amplitude but of increased duration, and combining said picture signals with said synchronizing pulses and said modified synchronizing pulses.

PHILIP J. HERBST. 

